The mechanisms underlying the growth of both normal and abnormal (malignant or defective) hematopoiesis have not completely been elucidated. While great strides in the purification of growth factors and some identification of target cells have been accomplished we have yet to determine how molecules are transferred via transmembrane signals to the nuclear machinary which in turn replicates the information of the genome to daughter progeny of hematopoietic stem cells. We have evidence that a macrocyclic lactone family of molecules can stimulate, either directly or via the secondary production of lymphokines by accessory cells, the growth of hematopoietic progenitors. These natural products purified to homogeneity from a marine animal Bugula neritina have the added property of being anti-neoplastic. We plan to determine the functional positive effects of these agents or normal and stem cell defective hematopoietic cells in animals and man and we furthermore will explore the inhibitory effects on tumor cells. Finally, we will attempt to determine the molecular biochemical mechanism of action of these materials on both normal and malignant hematopoietic cells.